So far, fluorescent lamps have been the main light sources used for illumination, and illumination devices which perform high frequency lighting using inverter lighting apparatuses have become widely popularized. Recently, LEDs have been attracting attention as being electrical light sources other than a discharge lamp which is represented as the fluorescent lamp. LEDs are superior to fluorescent lamps particularly in terms of life span, and it is expected that the efficiency thereof will exceed that of FHF32, that is, the main stream of fluorescent lamps for base illumination, thanks to future improvements in the technology.
Meanwhile, in a light source module in which a plurality of LEDs are mounted due to the development of the technology of LEDs, it is necessary to determine the number of LEDs used so that the light emitted from the light source module becomes almost constant and to determine whether to connect the LEDs in series or in parallel to each other. That is, it is required to appropriately determine a current value and a voltage value of the light source module by determining the number of LEDs used and the type of connection made between the LEDs.
Furthermore, also in a lighting apparatus for supplying current to the light source module, it is required to make a proper output in order to save power in accordance with the progress of the technology of LEDs. However, the current value and voltage value of the light source module vary depending on the electric characteristics of each LED, the number of LEDs used and series or parallel connection, which was described above. Accordingly, for example, there occurs the restriction in which the light source module should be configured to make the current value of the light source module constant (depending on the characteristics of LEDs, the number of LEDs used, and the type of connection between the LEDs) regardless of the advancements made in the technology of LEDs.
For example, it is assumed that there is a lighting apparatus having a light source module (hereinafter referred to as “LED module”) in which five LEDs have been connected in series. Herein, the voltage characteristic of each LED is 3.5 V, and the applied voltage of the LED module is then 3.5×5=17.5 V. When an LED module in which four LEDs having the same characteristic have been connected in series is connected to the lighting apparatus, excessive voltage is applied, so that excessive current flows.
Patent document 1 (Japanese Patent Application Publication No. 2009-224046) discloses a method for preventing failures attributable to the excessive current, in which a notification terminal for providing notification of an LED module being connected and disconnected is provided and the excessive current is prevented in response to a notification signal from the notification terminal. Furthermore, the configuration that maintains current outputted to the LED module at a constant level is provided.
Patent document 2 (Japanese Patent Application Publication No. 2009-21175) discloses a constant current circuit which has information about the electric characteristics of each LED module in which a plurality of LEDs have been mounted and provides constant current to each LED module. The information of each LED module is transferred to a lighting apparatus capable of supplying power to a plurality of LED modules, so that control is performed such that the output appropriate for the number of connected LED module is performed.
The example of the patent document 1 takes into account only the difference in the number of LEDs used, and does not consider the above-described advancements made in the technology of LEDs. For example, when the voltage characteristic of each LED is 3.5 V, the current characteristic thereof is 0.3 A and ten LEDs are connected in series, the applied voltage of an LED module is 3.5×10=35 V and the output current is 0.3 A. If, for example, the voltage characteristic of each LED is 3.0 V and the current characteristic thereof is 0.2 A thanks to the advancements in the technology of LEDs, the applied voltage of an LED module in which eight LEDS have been connected in series becomes 3.0×8=24 V. When seven LEDs each having a voltage characteristic of 3.5 V are connected in series, 3.5×7=24.5 V. The difference in voltage resulting from the difference in voltage characteristic and the difference in the number of LED used is not substantially large. However, by applying a current of 0.3 A to a LED having an output current of 0.2 A, the problem of abnormal generation of heat, a failure or a short life span attributable to excessive current is caused.
Furthermore, as a light source using LEDs, there have been proposed various types of light source modules which have the same pin base structure and the same lamp shape as linear fluorescent lamps and which can be installed on general illumination devices for fluorescent lamps. The two pin bases of a light source, such as a linear fluorescent lamp, will be referred to as a first pin base and a second pin base, respectively. While a fluorescent lamp is not lit up, the impedance of the first and second pin bases is almost infinite, so that a user replaces the fluorescent lamp in a state that the illumination device is being supplied with current. In this case, there occurs no risk although the user erroneously touches an electrode of the second pin base while inserting the electrodes of the first pin base into a socket of the illumination device. However, for a light source using LEDs, when, for example, the anode side is connected to the first pin base and the cathode side is connected to the second pin base, there is a worry over an electric shock if the electrodes of the first pin base are inserted into a socket and then user's contact with an electrode of the second pin base occurs upon the above-described replacement of the lamp.
Although the above-described patent document 1 does not describe a detailed technology for the structure of the LED module or an electrical connection structure of the LED modules, the patent document 1 adopts an output terminal mechanism in which conduction terminals to the LEDs and the notification terminals have been integrated. Accordingly, if a special and new connection structure is developed in order to prevent an electric shock from being occurring upon the replacement of the LED module, the worry over the electric shock can be avoided. However, it is necessary to invest in the development of the above-described LED module, the output terminal mechanism and a new illumination device in which the LED module and the output terminal mechanism can be installed.
In the patent document 2, the information that each LED module has is processed using a microcomputer. For example, a data table in which a plurality of pieces of information about the electric characteristics of LEDs, the numbers of LEDs, and connection type regarding series or parallel connection have been previously set to reflect the advancements in the LED technology may be provided, corresponding data may be selected in accordance with the characteristics and number of LEDs used, and the lighting apparatus may receive the data and output an appropriate current value.
If this technology is utilized, a lighting apparatus capable of dealing with future advancements in the technology of LEDs can be implemented, so that it is not necessary to maintain a constant total current of an LED module or to limit the characteristics, numbers and connection types of LEDs.
However, since it is necessary to install a data retention unit (a microcomputer or the like) and a control power source circuit for the data retention unit in each LED module, the configuration of the LED module is complicated, the cost of the LED module is increased, and the control power source circuit for the data retention unit installed in each LED module is difficult to configure.
To read information of each LED module before the LED module is lit up, a method of always outputting a voltage at a level at which the LED module cannot be lit up by means of the lighting apparatus and generating control power using the output voltage or a method of generating control power in the lighting apparatus and supplying the power to the LED module using another wire may be taken into consideration. The former method generates power loss because the lighting apparatus needs to be operated while the LED module is not being connected. The latter method causes the wiring between the lighting apparatus and the LED module to be complicated.
Furthermore, when the LED module is connected to the lighting apparatus, a connection structure or a socket structure is required so that a current supply line to the LEDs and a signal line from the data retention unit can be connected to each other without causing an error. In addition, when the LED module is replaced, it is desirable to provide a configuration which enables a user or a worker to relatively easily replace the LED module. Since the conventional technology does not provide a specific technology for configuring an electrical connection nor a specific technology for the structure of the LED module, there is a worry over the electric shock when the LED module is replaced. In order to provide countermeasures for the above worry, it is necessary to invest in new development, like in the case of the patent document 1.